Altimeter



` ocr. 3o, 1945. 1 O. wElL 1 n 2,388,027

' ALTIMETER Filed Dee. 21, 1945 2 sheets-sheet 1 M inl if .1

wuwwto/o OTTO Wen.

o.3o,V 1945. o. WE". 2,388,027

ALTIMETER Filed Dec. 21, 1945 2 sheets-sheet 2 Patented Oct. 30, 1945 p i vUNITED `SIA'I'S PATENT OFFICE .',AL'rIME'rnn om weil, New Yurk, NJ. l A Appununn December 21:1943, sensi No. 515.175 Y :i claims. (cm3-387) This invention relates to instruments for the detection of variations lin altitude,f such instruments being commonly designated altlmeters. and being widely used upon aircraft to inform the operators thereof of the elevation of such aircraftabove sea level.

' Mam types'of altimeters'havefheretofore been designed or suggested, and numerous kinds have heretofore and are now in actual service. It is not a difficult matter tol provide an instrument which will accurately indicate variations in'altitude resulting directly and solely from variations in airpressure. Such an instrument includes as its principal element a pressure responsive means which records 4the actual pressure existing at all elevations. Itis known, however, that in the .determination by instrument ofthe elevation of a point above sea level the actual existing pressure at that point must not only'be known, but' that the temperature must also'beftaken into consideration. A standard and Awell-known for-.

mula for the determination of the `true altitudeat a given point above sea level is as follows: i l

` H awmmmfl.- L t 57(i,()001.9812H,` 1 `in which4 formula He is the true altitude, To is thetemperature existing at sea level, T. is the temperature existing at the altitude of the instrument or pointer, and H1 the'elevaton indicated'` by the pressure responsivemeans. This `iformulataires into consideration the mean temperature of the air. Obviously, if the mean air temperature were to remain constant the true Valtitude of the instrument at anytime wouldvary solely with the indicated height as determined by the pressure responsive means. "As the mean airtemperature does vary, however, as the l.height varies, any` altimeter which neglects to make allowancefor such `teinperlaiture variations` cannot accurately indicate true altitudes. Realizsponsiveelevation indicating mechanism, to automatically record temperature changes and to" modify the action of the pressure responsive indicating mechanism from time to time as variations of temperature occur, an altitude indicator provided for the inspection of a pilot or navigator indicating the true altitude, such indication be` ing based upon temperature as well as pressure, the need for temperature charts being thus obviated and the work of the navigator and pilot being greatly simplied. While it has heretofore been proposed that altimeters having pressure responsive means be so modified such Vinstruments have not, for one reason or another, been adopted and used and it is a further purpose of the invention to provide an instrument which is of such simple nature, and which may be so ruggedly constructed that its adoption and use will be assured. In the following specification, and inthe accompanying drawings, a preferred type of instrument is rather `diagrammatically shown. It will be appreciated by those experienced in the art, however, that the form of the invention which is disclosed is set forth by way of example only and that the `design and arrangement of its component elements may be considerably modified without departure therefrom.

In the drawings: Y

Figure 1 is a perspective View showing those portions of the improved altimeter which are vital and essential to itsoperation, the casing, bearing supports forthe several operating parts, and yother conventional elements being omitted for the sake of clarity;

Figure 2 is a plan view ofportion of the altimeter casing showingthe indicating Idials and pointers; i Y v Figure 3 is a plan 'viewlof portion of the mechanismshown in 'Figure `l, the purpose of this View being to illustrate the `movements `of cer-s tain partsof the mechanism as they would occur i ying this, aviators'havefheretoiorefoundt necesv in the event thatno variations in temperature were met with; l

Figure 4 is asimilar view, the influence upon the indicatingV mechanism of the temperature responsive means being indicated; t t Figure 5 is a diagram indicating the movements of the controlling levers of Figure 4 and forming a basis for certain mathematicalderivations; and 1 Figure (i` is a .plan view of a. dial arrangement which may be employed with the altimeter instead `o1' the one shown inFigure 2.

The instrument will, ofcourse, include one or more-pointers to indicate the true altitude of the instrument and a pointer of `this type is ind i'` cated Aby the reference numeral I0, the dial over which the pointer plays being diagrammatically indicated at Illa in Figure 2. The hub of the Y pointer or indicating hand I is mounted upon `a short shaft Il supported by bearings, not illustrated, for rotation about a xed axis. A spring, such as the spiral spring I2, normally tends to turn the shaft I I in one direction and to move the pointer I0 toward a predetermined zero position. Rotation of shaft I I and movement of the pointer I0 in the opposite direction Iisbrought about by means of the movement of the circular rack I3 in a plane transverse to the shaft I I, the teeth of circular rack I3 meshing with those of a pinion I4 fixed upon shaft II.

Circular rack I3 is in turn xed upon a. shaft l5 disposed parallel to shaft II, and suitably supported for rotation about its own axis .by bearings, not illustrated. Upon shaft I5 arm I1. This arm may be vsaid to comprise a driven member adapted to receive a driving force imparted thereto by a thrustrod I8 the end of which is bifurcated as clearly shown in Figure l, the arm I1 lying at all times between the arm of the bifurcated portion and the thrust rod I8 being adapted to apply a driving or operating force upon the rod I1 at various points along its length, rod It` being mounted in such manner that it may be bodily shifted in a plane normal to the axis of shaft I5 so that its bifurcated end may be moved along arm I1.

The thrust rod I8 is -pivotally connected at 20' and 2I' to the outer or free ends of the parallel arms and 2l, these arms being generally parallel to the arm I1, being equal in length, and the ends thereof remote from thrust rod I8 being nxed in hubs 22 and 23 respectively, these hubs being rotatable aboutparallel axes which are parallel to the axes of shafts I5 and I I. Hub 22 is mounted-upon a shaft 24k which is supported byrbearings, not illustrated, in fixed position, whereas, hub 23 is so mounted on the lever mem- VVber 35 thatit may be shifted in a plane which includes the arms 20, 2I, and I1, and valong a line in this plane which is substantially parallel to the arm I1, shifting of hub 23 therefore causingtravel of the bifurcated end of the thrust rod I8V longitudinally along the arm I1 and thus varying the distance of the pointof application of force to the arm I1 with respect tothe axis of the shaft I5, as -willjbe presently describedvin detail.

Any suitable pressure responsive means Vmay be employed and in the form of theinvention illustrated by way of example a pressure responsive device of the bellows type is indicated at 26, the movable element 21 of this device being connected by means of a link 28 to the outer or :free` end of an arm 29, fixed on the hub 38, hub 30 being in turn xed upon shaft 24. A With this arrangement it is clear that the pointer I0 will inf dicate movementsrof the member 21 of the pressureresponsive means in the instrument, motion of this member being communicated through the intermediate connecting parts, just described whenever the member 21 moves in either direction. Assuming that member 21 moves to the left (Figure l) through expansion of the bellows 26, the action of link 28 and arm 29 will be such as to cause counterclockwise rotation of the shaft 24 and movement of the thrust rod I8 toward the right, the force applied to arm ll'effecting movement ofthe circular rack I3 in a counterclockwise "direction, resulting in movement of the pointer I.,0;fin a clockwise direction and windisY mounted a hub I6 carrying a laterally extending.

` at all times.

effective to cause the arm I1 to follow the end of the thrust rod and to maintaincontact between the arm I1 and the. end of the thrust rod During this operation the hub-23 simply revolves idly with respect to its supporting arms 35 and the arm 2I performs guiding and supporting functions only, imposing nodriving orretarding force upon the thrust rod I8.

The temperature responsive mechanism, the function of which is to modify the action of the mechanism so far described so that the pointer I0 will be caused to indicate the true altitude, serves to shift the hub 23, arm 2|, and thrust rod I8 automatically in response to variations in temperature so that the point of contact between the bifurcated end of the thrust rod I8 and the arm I1 will be varied. Obviously the angular movement of pointer YIll will be decreased, for a, given movement of member. 21, if the bifurcated end of thrust rod VI8 is shifted outwardly along arm I1, and will be increased if the bifurcated arm of thrust rodVIB is shifted inwardly along arm I1. 'Ihe temperature responsive means, therefore, is so connected to the hub 23 as to effect this shifting movement in an f entirely automatic manner so that the effect of the mean temperature of the atmosphere in which the instrument nds itself will be fed into the machine automatically. This temperature responsive mechanism includes a lever member 35, preferably comprising parallel arms andl spacing posts, and mounted for movement 1n a plane normal to shafts II, I5, and 24 by suitable supporting means (not illustrated).

Lever member 35 is provided with a relatively long arm 35 at one end which pivotally supports the hub 23 and the relatively short arm 352 atx its opposite end which carries a short spindle 36 upon which a roller 31 is rotatably mounted. The arms 351 and 352 are disposed at right angles to the main lportion of the lever 35, which comprises'spaced parallel members 353 each of which is provided, intermediate its ends, with an enportion to reand this arm is so supported by guide `means which is not shown that it may be moved in the direction of its length when cam 42 is revolved, thus shifting hub 3s, errecting xmwementofV the lever 35 and movement of the-hub 23 pivotally l attached to the end of arm 35 of the lever.

Roller 31 at all times rests against the face ofV a cam 44, so that cam 44 comprises a base preventing movement of the end of the lever which'v carries roller 31 when cam 42 is active.'Y Like-- wise c am 42 comprises a base which prevents movement of the arm 40 and of the hub 39 when cam 44 lis revolved about a vertical axis. It thus` appears that lever 35 has a, shiftable ful'crum Vand means for effecting shifting movement -Vof Ythe fulcrum inrthe plane of the lever, likewise an actuating cam 44 which, when operated,will effect rocking movement of the lever about it's fulcrum. The cam follower portions of the lever' 3l are urged in the direction of their respective cams as by means of a spring 43.

The cam 44 is mounted upon the vertically supported shaft 45 the lower end of which is operatively connected by means of a pinion 4B and` circular rack 41 to the end of a temperature` responsive member 48 of anyconventional type, sulciently sensitive to indicate accurately small variations in temperature and sufficiently strong in action to apply a substantial torque to the shaft 45, so that cam 44 may rock lever 35, effecting shifting of the hub 23 and hence eiecting movement of the bifurcated endf ofthe thrust rod `III `along the arm I1. It will be understood that the end of thrust rod I8 remote from the bifurcated end, is pivoted to `the arm 20 and that the movement of thrust rod I8 is `an angular movement about this point of pivotal connection.

The spiral torsion spring 50 has one end secured to shaft 45 and normally tends to rotate this shaft in one direction, this spring opposing the action of member 48 and restoring the shaft when member 48 recedes. Upon the upper end of shaft 45 is a temperature indicating pointer 5| which is adapted to play over a scale 52, shown ln Figure 2. Encircling the shaft 45 is a sleeve 53 carrying a second pointer 54a`nd a small gear 55 the teeth `otwhich `mesh at `all times with `those of a pinion56 fixed on vertical shaft 51 to the lower end of which the cam 4'2 is secured.

A-tits upperend the shaft "51 is provided with a knurled hand-1e 58 by means of which theoperator` canfrotate the cam 42 Yand thus at the same time move the pointer 54 over thefscale 52.

It has been previously explained that the instrument forming the subject of the present invention is designed to indicatetrue altitude, by means of the pointer IIJ.` This involves applying'what amountsto two corrections, one for the temperature at the flight altitude, and the other in accordance with the temperature at sea level. The ilrst` correction is automatically registered in the instrument itself, while in the illustrated embodiment, the correction for temperatureat sea level is set by the pilot who receives the weather reports before and during flight. vActu-'- ally the instrument, by means of the floating lever `35 and.` its connections, resolves these two i temperature correctionsland produces a component-motion which corrects the reading of the pointerlaccording to the mean temperature between the flightV level andsea level.'

In setting -up the instrument, it is adjusted so asfto indicate the true altitude at say `15 C. In thiscondition, the arrangementis such that the pivot points or axes of the hubs 22, 23, and I6 are, in alignment. Then in use, the pointer 54 is set by means of the knob 58 to apoin't on -the dial 52 indicating the temperature at sea level. During this setting, the cam 42 will act upon the follower projection 40 carried by thecompound floating lever 35 and will give 'it-a movement inone direction or the other to affect the angularity of ,the thrust rod I8. Of course, at the same time the temperature indicating device 48 willA rotate the cam'44 which will apply to the floating lever` a movement whichfis also transmittedto the thrust rod.` These movements yare compounded by the lever 35and the resultant indicative of the mean temperature is applied toithe thrust rod.

If the `instrument changes altitude; but the meantemperature does not change, the reading of the pointer I0 will then reiiect only the movements of the element 21 of the pressure respon# sive device. If, as practically always happens, the temperature varies as well as the altitude, the cam 44 automatically revolves about the axis of shaft 45, thrusting away from shaft 45 the adjacent end of the lever and thus bodily shifting hub 23 in the opposite direction, the fulcrum of the lever, which passes through hub 39, remaining xed. The outward travel ofthe bifurcated end 'of the thrust rod I8 along the arm ward the axisof shaft I5 and increase of the `angular movement of the pointer I0 for a given linear movement of member 21 and the pressure responsive means 26.

In Figures 3 and 4 of the drawings the thrust rod I8 is shown in different positions. In Figure 3 this rod is shown, in full lines, in one position, and a position which it will occupy as it is longitudinally shifted to indicate changes in pressure without changes in temperature, is indicated by the dot-dash lines, the assumption being that the pressure has changed without change in ternperature. In Figure 4 the same elements are shown and it is assumed that the pressure responsive means has imparted to the thrust rod I8 the same longitudinal movement as it has in Figure 3, the arm 20 having in each inst-ance been advanced through the angle a, indicated by the letters A, B, and C inFigure 3 and A', B',

. C' in Figurei.

Arocked by the cam 44,'as,shown in Figure 4, the

thrust rod I8 will be rocked outwardly because of movement of the hub 23 through an angleY such as indicated at fp as shown, the bifurcated end of the thrust rod being shifted outwardly along the arm I1. If we now assume that the arm 28 is rocked by the pressure responsive means through the angle a, indicated at A. B', C' in Figure 4, the arm I1 willbe rocked thro` gh a somewhat smaller angle` due to the outward shifting of the thrust rod I8,` this smaller angle being indicatedat G', H', K', the angle a through which arm 28 has been moved being indicated at G', H', L and exceeding the actual angle through which arm I1 has been rockedby the vsmall angle indicated at K', H'. L'. The angle through which the arm I1 is rocked, therefore, will differ from the angle e through which the arm 20 is rocked and may be said to be equal t-o the angle a plus the angle the angle being-either positive or negative `lepending upon the direction of movement of the thrust rod I8 along the arm,I1. l.

The angle which is the angle to be added to or subtracted from the angle a, and which isn automatically determined by the mechanism iustldescribed; canbe' determined actually by the following formula:

in which formula represents the angle through which the thrust rocl I8v is shiftedv by the temperature responsive means, the angle a represents the angular movement ofthe arm-20` which results from the operation of the pressure` responsive means, the letter e represents the total 1ength of the thrustrod la; the letter orepresents the length of the arm.2|l', which: isl always equalto-the length of thearm 2l, and:V is always one-fifth of the length of the thrust rod I8; In

the design of the temperature responsive means the lever 35 is so proportioned that its fulcrumis three-fifths of its length distant from thatend thereof which carries the roller 31' andl two-fths of its length distant from that end which is connected'to the hub 23. That portion ofthe thrust rod I8 which-lies between the end ofv arm4 2iV and arm I1 is one-eighth of the totallength ofV this rod.

The derivation of the formula set Yforth above will be understood from the following when read in connection with Figure of the drawings.

2a-s1n The two cams 42 and M aresomewhat similar in shape and each has a varying radius, these radii being given at any point by the following formulas.

For cam u..v y

Ream-'bwhere I R=radius of cam.'A a+b=maximumradius.

=3/2 c-tan6. a=constant. 9=angle in, radians, c=distance between 20' andof total length of rod). Y =angle throughwhich thrust rod l8r-is 211 along redl it The radius oi'rthe cam decreases at' al unformz ratefrom4 a maximum (a+b) toa minimuma (4) according to the above equation.

`For-camu',

e y R'v=(a'+b/ -b'; where v v'=radiusof cam.-

Inv Figure 6 there is illustrateda modified:

in which the indiciaare arrangedy in. circles and? thev adjusting knob 58 is disposed-t outside of; the

larger dial area. The pointer l0' sweeps-around;-

the outer dial 10b whichy isy graduatedl in-` thou# sands of feet while the hands 5|" andi 55"' corre-- 4sponding to hands 5|V4 andj 542 of` Figure 2. sweeparounda smaller inner dial 52' graduatedfin: de'-,

grees of temperature. The-mechanicalconnections -inthis embodiment are the same or the equivalent of those previously described inconnection withV the iirst'embodimentV l Various other changes andi modifications mayV bemade in the embodimentsillustrated andi de-y scribed herein without departing, from the scope of the invention as defined' by the followingV claims.

Having thus described the invention, what is claimed as newand desired'to be securedv byLetf ters Patent is:

ne'ctedto the, ends of parallel armsmountedon;v

1. In aninstrument of the class described. inV combination, means responsive tov changes in altitude for indicating such changes, said means including an elongated thrust rodpivotally con-V hubs rotatable,respectively, about parallel axes; andv an indicator arranged to be actuated when the thrust rocl is reciprocated, and temperature controlled means for bodily shifting one of said-- hubs toangularly adjust the position ofl therdr about the other hub, for thevpurpose setforthf Y 2. In Yaninstrument oi the classdescribedpin combination,4 an altitude indicating; member.:

means responsivel to changes in altitude. oi the instrument for actuating said memberV to cause the samel to indicate-such changes', said means includinglan arm supported for movement about a fixed axis, a thrust rod for applying an operating force to said arm, said thrust rod having one end positioned to engage said arm at variousdis tances from said axis, a Vcarrier for the, other f end iof the thrust rod, by means ofv which the rodv maybe moved longitudinally to act upon and.

move said arm, and-mechanism movable. automatically in respecty to variations in temperature at the instrument, means for applying anv ad'.- justment to said mechanism inV accordance withv the temperature at sea level, and. meansuperatively connecting said mechanism with said Ithrust` rod to vary the point of contact therewith along said arm as the mean of said temperatures varies.

3. In an instrument of the class described, in combination. an altitude indicating member, means responsive to changes in altitude of the instrument for actuating said member to cause y the same to indicate such changes, said means including an arm supported for movement about a xedaxis, a thrustrod for applying an operating force to said arm, said thrust rod having one end positioned to engage said arm at various distances from said axis, 4a carrier for the other end of the thrust rod, by means of which the rod may be moved longitudinally to act upon and move said arm, and correction mechanism comprising a floating lever. means operatively connecting a point on said lever with said vthrust rod, means movable in response to variations in temperature at said instrument and disposed in contact with saidv floating lever at another point,`

and means adapted to be moved to accord with variations in temperature at sea level, and disposed in contact with said oating lever at still another point. whereby a` movement which is the resultant of those given the lever by the means movable in response to variations in temperature and means adapted to be moved 'toaccord with variations in temperature at sea level `is given to the thrust rod .to vary the point of arm.

contact therewith along the said O'I'I'O WEIL. 

